1. Field of the Invention
The present invention relates to a portable apparatus, such as a laptop type or portable type computer having a flat panel type display unit mounted detachable to a base unit. More particularly, this invention relates to a structure of a display unit having a voltage converter built therein.
2. Description of the Related Art
Recently, laptop type computers are popular which have a keyboard and a flat panel type display unit mounted to a base unit having a rectangular box shape.
Of portable computers of this type, the one having a display unit with a liquid crystal display (LCD) detachably connected to a base unit is disclosed in U.S. Pat. No, 4,749,364. According to the computer with the detachable display unit, when an image with a high resolution is desired, an operator detaches the display unit from the base unit and connects a CRT display unit to the base unit by a cable.
with this portable computer in use, to connect the display unit detachably, a socket having a first connector is provided to the base unit. The display unit has an engage leg having a second connector in association with this socket. Plugging the engage leg into the socket connects the connectors together to thereby mechanically and electrically couple the base unit and display unit.
The display unit uses a battery on the base unit side as its driving power supply. In a case where an LCD with a back light or plasma display is employed in the display unit, burning on the back light or generating a plasma discharge requires a voltage converter to convert the reference voltage of the battery into a high voltage. When this voltage converter is located on the base unit side, the first connector in the socket receives a high voltage through the voltage converter. The first connector, which is applied with the high voltage, is exposed in the socket when the display unit is detached from the socket. The operator, when accidentally touching the first connector, probably receives an electric shock.
According to computers with a detachable display unit, it is desired that the voltage converter be attached to the display unit side as disclosed in U.S. patent application Ser. No. 07/406,614 filed Sep. 12, 1989 by Takashi Hosoi.
The voltage converter includes circuit parts, such as a transformer and resistors, which generate heat themselves while being energized. Accommodating the voltage converter in the housing of the display unit therefore raises the following problem.
When using the computer, the operator sets the display unit upright for easier view of the LCD. If the voltage converter is located below the LCD when the display unit stands upright, heat generated by circuit parts rises due to the convection in the housing and is locally transmitted to the LCD. This produces color spots on the display screen due to the temperature difference, making it difficult to see an image.